The virtualization of a server computer (hereinafter referred to as server virtualization) is technology for allowing plural operating systems (hereinafter referred to as OS) to operate at the same time on a single physical computer. Logical partitioning, which is performed through a management program (server virtualization program) that splits resources of a physical computer into plural logical partitions (LPAR), is technology for allowing one OS (guest OS) to operate on each LPAR. The server virtualization program is a program that operates in a server virtualization layer (hereinafter referred to as a host OS), such as hypervisor and an OS different from the guest OS on the physical computer.
In the physical computer (server virtualization environment) that uses such logical partitioning, since any LPAR can be brought into use as an equivalent logical computer by the server virtualization program, the user can, on any LPAR, run a guest OS and applications on the guest OS. Thereby, the user can freely decide a position to execute a guest OS according to the load.
On the other hand, in the physical computer (server virtualization environment) that uses logical partitioning, since resources of the physical computer are shared by plural LPARs, a failure in resources of the physical computer could cause plural LPARs to fail.
Therefore, when a computer system having high availability is built in a server virtualization environment, a computer system is used which takes over (failover) an application program (hereinafter referred to as an application) having been operating on a guest OS to a guest OS of a different standby system when a failure occurs.
In “VMware (registered trademark) R Server Integrated Solution Using CLUSTERPRO (registered trademark)”, [online], issued by NEC Corporation, retrieved on Oct. 31, 2006, Internet <URL:http://www.ace.comp.nec.co.jp/CLUSTERPRO/clp/doc/pp_lin/CLUSTERPRO_VMware.pdf>, as cluster configuration methods in server virtualization environments, two methods are realized. As a first method, with a cluster program running on a guest OS on each LPAR, each cluster program on the guest OS monitors failures of the guest OS and AP on the other, and performs failover of AP. As a second method, with a cluster program running on a host OS, each cluster program on the host Os monitors failures of the host OS and the guest OSs on the other, and performs a failover of the guest OS.
With the first method, the cluster programs on the guest OSs monitor failures of the guest OSs and APs by communication (heartbeat) to perform failover to a standby system when a failure occurs in an active system in which the APs are operating. This failover method realizes hot standby that guest OSs and APs are previously activated in a standby system.
On the other hand, with the second method, the cluster program on the host OS monitors failures of the host OS and the guest OS by heartbeat so that, when a failure occurs in an active system, a standby system as a failover destination is booted by a guest OS on an identical computer or a different computer to perform failover. This failover method realizes cold standby that begins with the activation of a guest OS.
In U.S. Pat. No. 6,985,937, technology for dynamically guaranteeing the performance of applications on guest OSs in a server virtualization environment is described. According to the technology, the load on the guest OSs is monitored, and during overload, resources of a required guest OS are dynamically changed. Moreover, another technology is also described. According to the technology, during the resource change, when there are no allocatable resources in a physical computer in which a guest OS is run, by migrating the guest OS to a different physical computer having allocatable resources, resources of the guest OS are dynamically changed.